Use of non-digitized diffractive optical elements for high-throughput and damage-free laser materials processing

As a means to accomplish high-throughput and damage-free processes, non-digitized diffractive beam splitters are effectual: they can afford to fully suppress undesired diffraction beams by containing as much light energy as possible in a fan-out of beams meant for the process. The surface-relief structures of the splitters are designed using a Fourier- iterative algorithm and are formed on high-quality fused silica substrates using direct laser writing and reactive ion etching. For a 13-beam splitter, for example, a non-digitized element gives an efficiency of 97% with SN=38, whereas a binary counterpart is as efficient as 78% with SN=5, where SN is defined as the ratio between the minimum of the fanout beam intensities and the maximum of higher-order diffraction intensities. We have tested these two types of elements in laser-cutting experiments and verified that the non-digitized element is far superior to the binary element.